Dyestuff-bleaching preparation for the photographic silver dyestuff-bleaching process

ABSTRACT

In a photographic silver dyestuff-bleaching process a dyestuffbleaching preparation is used which contains an acid, a watersoluble iodide, optionally a dyestuff-bleaching catalyst and in addition a reductone such as ascorbic acid. These preparations, preferably in the form of baths, are distinguished by their stability and effectiveness even after prolonged storage in open containers.

United States Patent [7 2] inventors Matthias Schellenberg Fribourg; Max Marthaler, Marly-le-Petit, both of Switzerland [21] Appl. No. 834,445

[22] Filed June 18, 1969 [45] Patented Nov. 16, 1971 [7 3] Assignee Ciba Limited Basel, Switzerland [32] Priority June 25, 1968 [33 Switzerland [54] DYESTUFF-BLEACHING PREPARATION FOR THE PHOTOGRAPHIC SILVER DYESTUFF- BLEACHING PROCESS 5 Claims, 5 Drawing Figs.

[52] US. Cl 96/53,

Primary Examiner-J. Travis Brown An0rneysl-larry Goldsmith, Joseph G. Kolodny and Mario A. Monaco ABSTRACT: In a photographic silver dyestuff-bleaching process a dyestuff-bleaching preparation is used which contains an acid, a water-soluble iodide, optionally a dyestuffbleaching catalyst and in addition a reductone such as ascorbic acid. These preparations, preferably in the form of baths, are distinguished by their stability and effectiveness even after prolonged storage in open containers.

PATENTEUNUV 16 ISTI 3,520,744

SHEET 1 0F 3 PATENTEDNUV 16 I971 3 20 744 sum 2 or 3 LOG E PATENTEDNHV 16 IBH 3 520 744 SHEET 3 BF 3 L06 E FIG. 5.

DYESTUFF-BLEACHING PREPARATION FOR THE PHOTOGRAPHIC SILVER DYESTUFF-BLEACHING PROCESS The present invention relates to dyestuff-bleaching preparations for the treatment of photographic material according to the silver dyestuff-bleaching process. Preferably these colorbleaching preparations are in the form of baths.

The known dyestuff-bleaching baths for this process generally consist of an acid such as, for example, hydrochloric acid, a complex-forming agent such as, for example, thiourea and optionally a color-bleaching catalyst such as, for example, 2,3-diaminophenazine.

Among the disadvantages of the baths hitherto used it is to be emphasized especially at higher temperatures, that they change greatly, even when 'not being used, through oxidation or hydrolysis of their constituents, and that they dissolve reaction products such as, for example, silver salts out of the photographic materials to be treated, whereby their activity is changed and they can only be regenerated with difficulty in extended operation.

The present invention, therefore, relates to a dyestuffbleaching bath which does not possess the above disadvantages.

lt has already previously been proposed to add iodides as complex-forming agents to bleaching baths (compare British Patent Specification 535,130, corresponding to US. Pat. No. 2,217,544, and German Displayed Specification 1,158,368), but the results obtained with these baths are not reproducible since the baths are exhausted already after brief use or brief storage. It has now been found that color-bleaching preparations which contain an acid, a water-soluble iodide, a reductone and optionally a color-bleaching catalyst do not possess the disadvantages mentioned.

The present invention thus provides a dyestuff-bleaching preparation for the photographic silver dyestuff-bleaching process which contains an acid, a water-soluble iodide, optionally a dyestuff-bleaching catalyst, and a reductone.

The advantages of the dyestuff-bleaching preparation according to the invention become particularly obvious if the preparation is employed in continuous operation and at an elevated temperature.

Suitable acids are, for example, sodium hydrogen sulfate, sulfamic acid, acetic acid, citric acid, organic sulfonic acid or especially strong acids, for example, hydrochloric acid or sulfuric acid.

The water-soluble iodide can be, for example, potassium iodide, sodium iodide, ammonium iodide or hydriodic acid.

The dyestuff-bleaching catalyst can either be dissolved in the color-bleaching preparation or be contained in the photographic material to be bleached and can be, for example, a pyrazine, a quinoxaline or a phenazine.

Amongst the reductones, aci-reductones are preferred. The aci-reductones preferably correspond to the tautomeric for- R represents an optionally substituted aryl residue or a residue of formula R,CH,(CHOH),--, wherein n is an integer of from i to 4, and R, represents a hydrogen atom or a hydroxyl group if n=2 to 4 and a hydroxyl group if n=l.

Especially suitable aci-reductones are also cyclic or acyclic compounds which contain a 3-carbonyl-endiol-(l ,2) grouping offormula (2) m (EH 0 Suitable reductones are, for example reductinic acid, triose reductone, 3-hydroxy-5-phenyltetrone-acid, 3-hydroxy-5- phenyl-tetronimide, 5-o-chlorophenyl-3-hydroxy-tetronimide, isoascorbic acid and preferably ascorbic acid, or mixtures of these reductones.

The reductone to be employed should be appropriately so chosen that the normal potential or reductone/dehydro-reductone is more negative under the conditions chosen than the normal potential iodine/iodide. The effective potentials can also be varied by changing the quantity ratios.

At pH=l the following normal potentials are measured against a normal hydrogen electrode:

l 2l +536 mv. Ascorbic acid dehydroascorbic acid 330 mv. Reductinic acid dehydroreductinic acid +420 mv.

Triosereductone dehydrotriosereductone +220 mv.

in other words, this means that the dyestuff-bleaching preparation should, at a pH-value of 1, contain a reductone which has a normal potential reductone/dehydroreductone of less than 500 mv.

Since the potential l /2l is pH-indcpendent, but the potential reductone/dehydro-compound becomes more positive as the pH declines, it follows that in strongly acid baths more reductone must be present than in weakly acid baths. In general, it is sufficient to use within the range of from l to 10 mol percent of reductone relative to the amount of iodine presentfl'his is especially proved for reductones of which the potential at pH=0 is still more negative than that of iodine, as in the case of the above-mentioned reductones themselves.

The dyestuff-bleaching preparation can, apart from being in the form of a bath, for example also be in the form of a gellike thickener, in the form of a colloidal composition or of a photographic layer. By suitable technical measures such as, for example, the application of protective layers or encapsulation of the active components, the dyestuff-bleaching preparations can be introduced into a photographic material in such a way that the dyestuff-bleaching action can only develop on processing the photographic material. In Special cases mix tures of iodides and reductones as such can also be present, whilst the acid and the dyestuff-bleaching catalyst are accommodated in another phase (compare for example French Patent Specification 1,504,238

In the known baths containing iodide, which do not contain any reductone, reasonably reproducible results can at most be obtained if working with complete exclusion of air. Exposed to air, such a bath however rapidly darkens, is corrosive and loses bleaching power, so that the resulting color images become flatter and flatter and can finally no longer altogether be fully bleached. Baths containing reductone can on the other hand even be stirred with air and yield results which always remain constant over a long period.

When using a dyestuff-bleaching preparation according to the invention for bleaching reducible image substances, for example, azo dyestuffs, nitro dyestuffs and diazonium salts in the presence of metallic images, these metallic images can, by a method known per se, be the converse of the original, (negative) or the same as the original (positive). It is appropriate that after the development and before the bleaching all metal salts which may possibly still be present, for example, silver chloride or silver bromide should be dissolved out of the material (fixed) since otherwise the iodide content of the dyestuff-bleaching bath would rapidly become exhausted and major amounts of sparingly soluble silver iodide would form at the same time. After the dyestuff-bleaehing bath would rapidly become exhausted and major amounts of sparingly soluble silver iodide would form at the same time After the dyestuff-bleaching the remaining silver IS removed by a method known per se.

The color-bleaching baths can, in addition to the constituents mentioned, contain one or more usual additives, for example, complex-forming agents, wetting agents and solvents The following Examples illustrate the invention; the percentages denote percentages by weight.

EXAMPLE 1 A silver bromide emulsion dyed with a dyestuff of formula H 8 SO H OCH;

is cast in the usual manner on a film carrier, exposed behind a step wedge and processed as follows at 24 C:

1. Development, 6 minutes: 2 g. of p-methylaminophenol sulfate 50 g. of anhydrous sodium carbonate, 2 g. of potassium bromide and water to make up to 1 liter.

2. Stop bath, 1 minute: g. of crystalline sodium acetate, g. of glacial acetic acid, and water to make up to 1 liter.

3. Fixing, 4 minutes: 20 percent strength solution of sodium thiosulfate.

4. Soaking, 10 minutes b 5. Dyestuff bleaching, 8 minutes: 500 ml. of water, 27 ml. of sulfuric acid (96 percent strength), 0.2 g. of ascorbic acid, 20 ml. of a mixture of benzyl alcohol (40 percent), diethylene glycol (40 percent and water (20 percent) 10 mg. of 6- benzoylamino-Z,3-dimethyl-quinoxaline, 10 g. of potassium iodide and water to make up to 1 litre.

6. Soaking, 4 minutes.

7. Silver bleaching, 6 minutes: 500 ml. of water, 27 ml. of sulfuric acid (96 percent strength), 20 g. of crystalline copper sulfate, 60 g. of potassium bromide and water to make up to 1 liter.

6. Soaking, 4 minutes.

7. Silver bleaching, 6 minutes: 500 ml. of water, 27 ml. of sulfuric acid (96 percent strength), 20 g. of crystalline copper sulfate, 60 g. of potassium bromide and water to make up to 1 liter.

8. Soaking, 4 minutes.

9. Fixing, 4 minutes: 20 percent strength solution of sodium thiosulfate.

l0. Soaking, 10 minutes.

ll. Drying.

In this way a color image in the same sense as the original (positive) is obtained, the gradation of which is reproduced in curve 1. It will be seen from this curve that the dyestuff can be completely bleached.

If the dyestuff-bleaching bath (5 of the above composition is left standing for 4 days in an open vessel and the process is then repeated, an identical bleaching, also corresponding to curve 1, is achieved.

if a dyestuff-bleaching bath (5) is used which does not contain any ascorbic acid, various results depending on the age of the bath are obtained. In the freshly mixed bath a bleaching is achieved which coincides with the color gradation curve 1. Since this curve is only of poor reproducibility, it has not been shown separately on the table of curves. If the bath is allowed to stand for 4 days without ascorbic acid and is then used for bleaching, the gradation corresponding to curve 2 is obtained. It will be seen from the curve that a complete dyestuff bleaching can no longer be achieved.

EXAMPLE 2 The procedure of example i is followed but a color bleaching bath is used which instead of the ascorbic acid contains l g./1. of triose-reductone. The triose-reductone is obtained by reacting lead reductonate (according to Euler- Eistert, Chemistry and Biochemistry of the Reductones and Reductonates, Verlag Enke, Stuttgart 1957, page 53) with sulfuric acid and separating off the lead sulfate formed.

If the dyestuff-bleaching bath is immediately used, the same results are obtained as when using it after it has stood for 4 days in air.

It will be seen from gradation curves 3 and 4 that similar results to example I are obtained.

EXAMPLES 3, 4, 5 and 6 The procedure of example 1 is followed, but dyestuffbleaching baths of the following composition are used: 60 g. of sulfamic acid and l g. of iso-ascorbic acid (example 3) or 1 g. of 3-hydroxy-5-phenyltetrone-acid (example 4) or I g. of 3- hydroxy-5-phenyl-tetronimide (example 5) or 1 g. of 5-0- chlorophenyl-3-hydroxy-tetronimide (example 6); l0 mg. of phenazine; l7 g. of potassium iodide; water to make up to 1 liter.

If the dyestuff-bleaching baths are immediately used, the same results are obtained as when using them after four days standing in air.

If the dyestuff-bleaching bath without reduction is used for dyestuff bleaching after 4 days, complete bleaching of the dyestuff is no longer possible, as can be seen from curves 5 and 6.

EXAMPLE 7 The procedure of example I is used but the following dyestuff-bleaching bath employed: 60 g. of p-toluenesulfonic acid, 1 g. of ascorbic acid, 10 mg. of phenazine, l5 g. of ammonium iodide and water to make up to l liter.

It will be seen from the graduation curves 7 and 8 that similar results to example I are obtained.

EXAMPLE 8 The procedure of example 1 is followed but the following dyestuff-bleaching bath is used: 60 g. of sulfamic acid, I g. of ascorbic acid, 50 mg. of 2,5-dimethylpyrazine, l7 g. of potassium iodide and water to make up to 1 liter.

It can be seen from the gradation curves 9 and 10 that similar results to example 1 are obtained.

EXAMPLE 9 The procedure of example 1 is used, but the treatment is carried out for l2 minutes in a dyestuff-bleaching bath of the following composition: 5 g. of sodium acetate, 10 ml. of glacial acetic acid, 1 g. of ascorbic acid, 200 mg. of 2,3-dimethyl-6- methoxyquinoxaline, l60 g. of potassium iodide and water to make up to 1 liter.

If the dyestuff-bleaching bath is immediately used, the same result is obtained as when using it after 4 days standing in air. The dyestuff is completely bleached behind the lightest wedge step. if the dyestuffbleaching bath is made up without ascorbic acid, various results depending on the age of the solution are obtained. After 4 days standing in air, the dyestuff can no longer be completely bleached. A similar result is obtained if instead of the acetic acid-acetate combination a citric acid citrate combination is used.

EXAMPLE l0 A photographic material with three color layers has a gelatine layer containing the dyestuff-bleaching catalyst 2,3- diphenyl-6-aminoquinoxaline deposited on a carrier, a redsensitive silver bromide emulsion containing the bluish-green dyestuff of formula on top of this, and a green-sensitive silver bromide emulsion containing the purple dyestuff of formula:

This is followed by a silver bromide layer containing the yellow dyestuff of formula:

This copying material is exposed behind a step wedge and processed in accordance with example 1. The following bath is however used for dyestuff bleaching: 27 ml of sulfuric acid (96 percent strength), 0.5 g. of ascorbic acid, 25 g. of potassium iodide and water to make up to 1 liter A positive image of the step wedge is obtained in this manner, in which all three dyestuffs are completely bleached behind the lightest wedge step. The same result is obtained if this dyestuff-bleaching bath is used after 4 days standing.

if, however, the dyestuff-bleaching bath without reductone is used for dyestuff-bleaching after 4 days, it is no longer possible to bleach the three dycstuff to white.

EXPLANATION OF COLOUR GRADATION CURVES 1 TO 4 D Colour density Log E=Logarithm of the exposure Dyestufl bleaching bath with ascorbic acid, fresh and dyestufl bleaching bath with ascorbic acid, 4 days old.

Dyestufl bleaching without ascorbic acid,

4 days old.

D yestufi bleaching bath with triosereductone, fresh and dysetufi bleaching bath with triose-reductone, 4 days old.

Dyestutf bleaching bath without trlosereductone, 4 days old.

Dyestufi bleaching bath with rcductono fresh and dyestufl bleaching bath with reductone, 4 days old.

Dyestufl bleaching bath without reductone, 4 days old.

Dyestufl bleaching bath with ascorbic acid, fresh and dyestufl bleaching bath with ascorbic acid, 4 days old.

Dyestufi bleaching bath without ascorbic acid, 4 days old.

Dyestufl bleaching bath with ascorbic acld, fresh and dycstufl bleaching with acid, 4 days old.

Dyestufl' bleaching bath without ascorbic acid, 4 days old.

Curve 1...

Example 1 Curve 2..

Curve 3..

Curve 4...

Curve 5...

Examples 3 to 6 Curve 6..

Curve 7-.

Example 7 Curve 8...

Curve 9.

Curve 10..

We claim:

I. A dyestuff-bleaching preparation for the photographic silver dyestuff-bleaching process containing an acid, a water' soluble iodide, a reductone, and a dyestuff-bleaching catalyst, said reductone being selected from the group consisting of reductinic acid, triose reductone, ascorbic acid, isoascorbic acid, 3-hydroxy-5-phenyl-tetronic acid, 3-hydroxy-5-phenyl tetronimide, and 5-o-chloro-phenyl-3-hydroxy-tetronimide, said dyestuff bleaching catalyst being selected from the group consisting of a pyrazine, a quinoxaline and a phenazine.

2. A preparation according to claim 1 being in the form of a dyestuff-bleaching bath.

3. A preparation according to claim 1 containing as acid a member selected from the group consisting of an organic sulfonic acid, sodium bisulfate, hydrochloric acid, sulfuric acid, acetic acid and citric acid.

4. A preparation according to claim 1 containing as watersoluble iodide hydriodic acid, ammonium iodide, sodium iodide and potassium iodide.

5. A preparation according to claim 1 containing sulfuric acid, potassium iodide and ascorbic acid. 

2. A preparation according to claim 1 being in the form of a dyestuff-bleaching bath.
 3. A preparation according to claim 1 containing as acid a member selected from the group consisting of an organic sulfonic acid, sodium bisulfate, hydrochloric acid, sulfuric acid, acetic acid and citric acid.
 4. A preparation according to claim 1 containing as water-soluble iodide hydriodic acid, ammonium iodide, sodium iodide and potassium iodide.
 5. A preparation according to claim 1 containing sulfuric acid, potassium iodide and ascorbic acid. 